Comparison of the effects of xylazine bolus versus medetomidine constant rate infusion on cardiopulmonary function and depth of anesthesia in horses anesthetized with isoflurane

Comparison of Xylazine and Lidocaine Infusion versus Medetomidine Continuous Rate Infusion during General Anesthesia with Isoflurane in Horses Undergoing Emergency Laparotomy

(1) The main goals of general anesthesia include pain management and a safe anesthetic protocol for smooth recovery. In this retrospective study, we compared two anesthetic protocols for general anesthesia with isoflurane during emergency laparotomy: sedation with xylazine and the intraoperative infusion of lidocaine (X group) versus medetomidine as a preoperative sedation and intraoperative infusion (M group). (2) The medical records of horses who underwent emergency laparotomies between 2016 and 2023 were reviewed. According to the anesthetic protocol, patients were allocated to the X or M groups. Data about the horse, signalment, history, and anesthetic variables were analyzed. (3) Group X had a significantly higher heart rate (HR), lower respiratory rate (RR) and mean and diastolic arterial pressure (MAP/DAP). A progressive increase in HR and RR was observed in both groups. Group X underwent a decrease in RR and an increase in DAP. In Group M, a decrease in MAP and DAP was observed. Group M exhibited a longer recovery time with similar recovery scores. Both protocols provided safe anesthesia for emergency laparotomy, with minor cardiovascular and respiratory depression. Minor respiratory depression was detected when xylazine was used, while recovery was longer with medetomidine.

Total Intravenous Anaesthesia with Ketamine, Medetomidine and Midazolam as Part of a Balanced Anaesthesia Technique in Horses Undergoing Castration

To evaluate the use of ketamine-medetomidine-midazolam total intravenous infusion as part of a balanced anaesthetic technique for surgical castration in horses. Five healthy Standardbred cross colts were premedicated with IV acepromazine (0.01–0.02 mg/kg), medetomidine (7 µg/kg) and methadone (0.1 mg/kg) and anaesthesia induced with IV ketamine (2.2 mg/kg) and midazolam (0.06 mg/kg). Horses were anaesthetised for 40 min with an IV infusion of ketamine (3 mg/kg/h), medetomidine (5 µg/kg/h) and midazolam (0.1 mg/kg/h) while routine surgical castration was performed. Cardiorespiratory variables, arterial blood gases, and anaesthetic depth were assessed at 5 to 10 min intervals. Post-anaesthesia recovery times were recorded, and the quality of the recovery period was assessed. The anaesthetic period and surgical conditions were acceptable with good muscle relaxation and no additional anaesthetic required. The median (range) time from cessation of the infusion to endotracheal tube extubation, head lift and sternal recumbency were 17.2 (7–35) min, 25 (18.9–53) min and 28.1 (23–54) min, respectively. The quality of anaesthetic recovery was good, with horses standing 31.9 (28–61) min after the infusion was ceased. During anaesthesia, physiological variables, presented as a range of median values for each time point were: heart rate 37–44 beats/min, mean arterial pressure 107–119 mmHg, respiratory rate 6–13 breaths/min, arterial partial pressure of oxygen 88–126 mmHg, arterial partial pressure of carbon dioxide 52–57 mmHg and pH 7.36–7.39. In conclusion, the co-administration of midazolam, ketamine and medetomidine as in IV infusion, when used as part of a balanced anaesthetic technique, was suitable for short term anaesthesia in horses undergoing castration.

Clinical Randomized Comparison of Medetomidine and Xylazine for Isoflurane Balanced Anesthesia in Horses

Introduction: To assess drug plasma levels, preanesthetic sedation, cardiopulmonary effects during anesthesia and recovery in horses anesthetized with isoflurane combined with medetomidine or xylazine.

Study design: Prospective blinded randomized clinical study.

Animals: Sixty horses undergoing elective surgery.

Methods: Thirty minutes after administration of antibiotics, flunixine meglumine or phenylbutazone and acepromazine horses received medetomidine 7 μg kg⁻¹ (group MED) or xylazine 1.1 mg kg⁻¹ (group XYL) slowly intravenously (IV) and sedation was assessed 3 min later. Anesthesia was induced with ketamine/diazepam and maintained with isoflurane in oxygen/air and medetomidine 3.5 μg kg⁻¹ h⁻¹ or xylazine 0.69 mg kg⁻¹ h⁻¹. Ringer's acetate 10 mL kg⁻¹ h⁻¹ and dobutamine were administered to maintain normotension. All horses were mechanically ventilated to maintain end-tidal carbon dioxide pressures at 45 ± 5 mmHg (5.3–6.7 kPa). Heart rate (HR), invasive arterial blood pressures, inspired and expired gas compositions, pH, arterial blood gases, electrolytes, lactate and glucose were measured. For recovery all horses received intramuscular morphine 0.1 mg kg⁻¹ and medetomidine 2 μg kg⁻¹ or xylazine 0.3 mg kg⁻¹ IV. Recovery was timed and scored using three different scoring systems. Plasma samples to measure medetomidine and xylazine concentrations were collected at predetermined timepoints. Repeatedly measured parameters were analyzed using a two-way repeated-measures analysis of variance for differences between groups and over time; p < 0.05 was considered statistically significant.

Results: Mean arterial blood pressures (MAP) stayed within normal ranges but were higher (p = 0.011) in group XYL despite significant lower dobutamine doses (p = 0.0003). Other measured parameters were within clinically acceptable ranges. Plasma levels were at steady state during anesthesia (MED 2.194 ± 0.073; XYL 708 ± 18.791 ng mL⁻¹). During recovery lateral recumbency (MED 42.7 ± 2.51; XYL 34.3 ± 2.63 min; p = 0.027) and time to standing (MED 62.0 ± 2.86; XYL 48.8 ± 3.01 min; p = 0.002) were significantly shorter in group XYL compared to group MED. Recovery scores did not differ significantly between groups.

Conclusion and Clinical Relevance: In horses anesthetized with isoflurane and medetomidine or xylazine, xylazine maintained higher MAP, reduced the dobutamine consumption and recovery time, whilst overall recovery quality was unaffected.

Comparison of bispectral index and spectral entropy during isoflurane and medetomidine general anaesthesia in horses

BACKGROUND

The bispectral index (BIS) has been evaluated as an indicator of central nervous system (CNS) depression in horses during general anaesthesia. The spectral entropy is another electroencephalographic device and it has not been evaluated yet in horses.

OBJECTIVES

To determine if spectral entropy can assess anaesthetic depth during the different phases of anaesthesia, define the value of state and response entropy during surgical plane of anaesthesia and compare them with BIS.

STUDY DESIGN

Clinical, prospective, non-blinded observational study.

METHODS

Thirty-five horses ASA I or II undergoing scheduled surgical procedure were used. BIS and electromyography (EMG) with a BIS monitor and state and response entropy with a spectral entropy monitor were recorded at baseline after receiving 5 µg/kg bwt i.v. of medetomidine (sedation period), during the anaesthetic maintenance with isoflurane and medetomidine (intraoperative period) and once the trachea was extubated (recovery period). A general linear model for repeated measurements was employed. Correlation and agreement between methods were also assessed. Data are presented as mean ± SD.

RESULTS

State entropy, response entropy and EMG showed significant differences according to the anaesthetic period (P < .001). There was no significant difference in BIS between baseline and sedation period, but there were differences between the remainder of the periods (P < .001). BIS (53.4 ± 11.2) was significantly higher (P < .001) than response entropy (35.1 ± 7.1) and state entropy (27.4 ± 4.8) during surgical plane of anaesthesia. The ICC between BIS and response entropy was 0.56 and between BIS and state entropy was 0.43, without agreement between them.

MAIN LIMITATIONS

The need to shave the skin in contact with the sensors and the difficulty in taking measurements during recovery period.

CONCLUSIONS

Spectral entropy can be used to detect the different periods of an anaesthetic protocol, with the lowest values during the intraoperative period. A low correlation and no concordance were observed between both methods.

Clinical effects of constant rate infusions of medetomidine-propofol combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery

Background

The aim of the present study was to evaluate clinical efficacy of constant rate infusions (CRIs) of medetomidine–propofol combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery. Thirty horses were sedated intravenously (IV) with medetomidine (6.0 μg/kg) and midazolam (0.02 mg/kg) and induced IV with ketamine (1.0 mg/kg) and propofol (1.0 mg/kg). These horses were randomly allocated to three groups and maintained with sevoflurane and CRI of either medetomidine (3.0 μg/kg/h) (Group M; n = 10); or medetomidine (3.0 μg/kg/h) and propofol (3.0 mg/kg/h) (Group MP3; n = 10); or medetomidine (3.0 μg/kg/h) and propofol (6.0 mg/kg/h) (Group MP6; n = 10). End-tidal sevoflurane concentration (ET_SEVO), cardiovascular parameters, plasma propofol concentration, and recovery time and quality were compared among groups. Data were analyzed by using ANOVA with Tukey’s multiple comparison test, considering P < 0.05 significant.

Results

ET_SEVO (%) was 2.4 ± 0.1 in Group M, 1.7 ± 0.2 in Group MP3, and 1.4 ± 0.2 in Group MP6; ET_SEVO declined significantly in a propofol-dose-dependent manner. The rates of dobutamine infusion (μg/kg/min) required to keep the mean arterial blood pressure over 70 mmHg were significantly lower in Group MP3 (0.20 ± 0.10) and Group MP6 (0.15 ± 0.06) than in Group M (0.37 ± 0.18). Recovery time and quality did not differ among groups. All horses in Group MP3 required only one attempt to stand, and recovery quality was excellent. Plasma propofol concentrations were stable throughout maintenance of anesthesia in Group MP3, whereas those in Group MP6 increased significantly with increasing duration of maintenance.

Conclusions

CRIs of medetomidine–propofol reduced the sevoflurane requirement for surgical anesthesia as the propofol dose increased, compared with a CRI of medetomidine alone. Additionally, the two propofol protocols provided good maintenance of cardiovascular function. CRIs of medetomidine (3.0 μg/kg/h) and propofol (3.0 mg/kg/h) resulted in excellent-quality recovery. This protocol could therefore be an especially useful additive to sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery.

Clinical evaluation of constant rate infusion of alfaxalone-medetomidine combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery

Background

Alfaxalone has a number of pharmacological properties which are desirable for constant rate infusion (CRI). Previously, the co-administration of alfaxalone and medetomidine is shown to be suitable for short-term anesthesia in horses. However, the use of alfaxalone–medetomidine CRI with inhalational anesthesia under surgical procedures have not been investigated in clinical cases. The aim of the present study was to evaluate the clinical efficacy of alfaxalone–medetomidine CRI in sevoflurane-anesthetized Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane requirement, cardiovascular function, and induction/recovery quality were compared between horses maintained with sevoflurane in combination with medetomidine CRI (3 µg/kg/h) (Group M; n = 25) and those maintained with sevoflurane in combination with alfaxalone–medetomidine CRI (0.5 mg/kg/h and 3 µg/kg/h, respectively) (Group AM; n = 25).

Results

The mean end-tidal sevoflurane concentrations were significantly lower in Group AM (1.8 ± 0.2%) than in Group M (2.4 ± 0.1%). The mean dobutamine infusion rate required for maintaining mean arterial blood pressure within the target values (60–80 mmHg) was significantly lower in Group AM (0.53 ± 0.20 µg/kg/min) than in Group M (0.85 ± 0.32 µg/kg/min). Induction and recovery scores were not significantly different between two groups. However, excitatory response during recovery were observed in five horses in Group AM. The mean plasma alfaxalone concentrations were stable throughout the maintenance period (0.77 ± 0.12 to 0.85 ± 0.13 µg/mL), and decreased significantly immediately after standing (0.32 ± 0.07 µg/mL).

Conclusions

Alfaxalone–medetomidine CRI reduced sevoflurane requirement by approximately 26% with good maintenance of cardiopulmonary function in Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane in combination with alfaxalone–medetomidine CRI may be a clinically effective anesthetic technique for Thoroughbred racehorses. However, 20% of horses administered alfaxalone showed remarkable excitatory response during recovery. Greater attention to excitatory response may be advisable if alfaxalone is used for induction or maintenance of anesthesia. A larger study is needed to explore the clinical relevance of these findings.

Clinical usefulness of intravenous constant rate infusion of fentanyl and medetomidine under sevoflurane anesthesia in Thoroughbred racehorses undergoing internal fixation surgery

A total of 20 racehorses with longitudinal fractures underwent internal fixation surgery under sevoflurane anesthesia combined with infusion of medetomidine (3 µg/kg/hr) alone (10 horses, group M) or medetomidine and fentanyl (7 µg/kg/hr) (10 horses, group FM). In group FM, the end-tidal sevoflurane concentration during surgery was maintained significantly lower than in group M (2.8–2.9% for group M vs. 2.2–2.6% for group FM, P<0.01). The mean arterial blood pressure was maintained over 70 mmHg using dobutamine infusion (group M, 0.36–0.54 µg/kg/min; group FM, 0.27–0.65 µg/kg/min), and the recovery qualities were clinically acceptable in both groups. In conclusion, co-administration of fentanyl and medetomidine by constant rate infusion may be a clinically useful intraoperative anesthetic adjunct for horses to reduce the requirement of sevoflurane when they undergo orthopedic surgery.

Comparison of two analyzers to determine selected venous blood analytes of Quaker parrots (Myiopsitta monachus)

Point of care devices can assess electrolyte, blood gas, biochemical, and hematologic values in a critical care setting. Although these devices are commonly used in humans and companion mammals, few studies have assessed their use in avian species. This study compares electrolyte, hemoglobin (Hgb), hematocrit (Hct), acid-base, and venous blood gas parameters between the i-STAT and IRMA TruPoint blood gas analysis systems for 35 Quaker parrots. Agreement between the two analyzers and the effect of gender, time lag between sample analysis, and cartridge expiration were evaluated. Male birds had increased Hgb and Hct compared with females, independent of analyzer method. In expired i-STAT cartridges, only glucose significantly increased. Packed cell volume determined by centrifugation was higher than Hct, as calculated by either analyzer. The analyzers had good agreement for total carbon dioxide, bicarbonate, pH, and Hgb, fair agreement for potassium (K), ionized calcium (iCa), venous partial pressure of carbon dioxide, and base excess, and poor agreement for sodium (Na), venous partial pressure of oxygen (PO2), and oxygen saturation (SO2). Values for Na, iCa, PO2, and SO2 were significantly higher on the IRMA than the i-STAT, while K was significantly lower on the IRMA when compared with the i-STAT. The time lag between sample analyses on the i-STAT and IRMA did not be correlate to any analyte changes. Despite these differences, both the i-STAT and the IRMA appear to be acceptable clinical tools in avian critical care, although reference ranges for each analyzer should be created.

Effects of continuous rate infusion of butorphanol in isoflurane-anesthetized calves

PURPOSE

To assess the hemodynamic changes and bispectral index (BIS) following administration of a continuous rate infusion (CRI) of butorphanol in isoflurane-anesthetized calves.

METHODS

Eight calves weighing 110 ± 12 kg were included in the study. Anesthesia was induced with 5% isoflurane in O2 delivered via face mask and maintained with end-tidal concentration of 1.4%. IPPV was set to a peak inspiratory airway pressure of 15 cmH2O and respiratory rate of six breaths minute-1. Forty minutes after the start of anesthetic maintenance, 0.1 mg kg-1butorphanol was administered intravenously, followed by a CRI of 20 µg kg-1 minute-1. Hemodynamic variables and BIS were recorded before butorphanol administration (T0), and at 10, 20, 40 and 80 minutes following the CRI. Anesthesia was discontinued after the last recording and the calves were allowed to recover. The time to sternal recumbency (SRE) and standing (ST) were evaluated.

RESULTS

There were no significant differences between the moments in all hemodynamic variables and BIS. The time to SRE and ST was 9 ± 5 and 14 ± 7 minutes, respectively.

CONCLUSION

The continuous rate infusion did not produce clinically relevant changes in hemodynamic or bispectral index values compared to baseline in mechanically ventilated and unstimulated calves anesthetized at 1.4% isoflurane.

Cardiopulmonary effects of dexmedetomidine and ketamine infusions with either propofol infusion or isoflurane for anesthesia in horses

OBJECTIVE

To examine the cardiopulmonary effects of two anesthetic protocols for dorsally recumbent horses undergoing carpal arthroscopy.

STUDY DESIGN

Prospective, randomized, crossover study.

ANIMALS

Six horses weighing 488.3 ± 29.1 kg.

METHODS

Horses were sedated with intravenous (IV) xylazine and pulmonary artery balloon and right atrial catheters inserted. More xylazine was administered prior to anesthetic induction with ketamine and propofol IV. Anesthesia was maintained for 60 minutes (or until surgery was complete) using either propofol IV infusion or isoflurane to effect. All horses were administered dexmedetomidine and ketamine infusions IV, and IV butorphanol. The endotracheal tube was attached to a large animal circle system and the lungs were ventilated with oxygen to maintain end-tidal CO2 40 ± 5 mmHg. Measurements of cardiac output, heart rate, pulmonary arterial and right atrial pressures, and body temperature were made under xylazine sedation. These, arterial and venous blood gas analyses were repeated 10, 30 and 60 minutes after induction. Systemic arterial blood pressures, expired and inspired gas concentrations were measured at 10, 20, 30, 40, 50 and 60 minutes after induction. Horses were recovered from anesthesia with IV romifidine. Times to extubation, sternal recumbency and standing were recorded. Data were analyzed using one and two-way anovas for repeated measures and paired t-tests. Significance was taken at p ≤ 0.05.

RESULTS

Pulmonary arterial and right atrial pressures, and body temperature decreased from pre-induction values in both groups. PaO2 and arterial pH were lower in propofol-anesthetized horses compared to isoflurane-anesthetized horses. The lowest PaO2 values (70-80 mmHg) occurred 10 minutes after induction in two propofol-anesthetized horses. Cardiac output decreased in isoflurane-anesthetized horses 10 minutes after induction. End-tidal isoflurane concentration ranged 0.5%-1.3%.

CONCLUSION AND CLINICAL RELEVANCE

Both anesthetic protocols were suitable for arthroscopy. Administration of oxygen and ability to ventilate lungs is necessary for propofol-based anesthesia.